In mathematics, an open circle is used to represent a point that is not included in a set or on a graph. It is often used in inequalities and graphing to indicate that a particular value is not part of the solution set.
For example, if you see an open circle on a number line at the point x = 3, it means that 3 is not included in the set of solutions. This is commonly used in inequalities like x > 3, where 3 is not part of the solution.
On a graph, an open circle at a point (a, b) indicates that the point (a, b) is not included in the graph of the function. This is often seen in piecewise functions or when graphing inequalities.
In summary, an open circle is a visual representation that a specific value or point is excluded from a set or graph.